1. Field of the Invention
The present invention relates to an inkjet printhead. More particularly, the present invention relates to a piezoelectric inkjet printhead manufactured from two silicon substrates, and a method of manufacturing the same.
2. Description of the Related Art
An inkjet printhead is a device that ejects fine ink droplets onto a desired position of a print medium in order to print an image of a predetermined color. Inkjet printheads may be roughly classified into two types according to the ink ejection method used. The first type is a thermally-driven inkjet printhead that generates bubbles in ink using a heat source and ejects ink using an expansion force of the bubble. The second type is a piezoelectric inkjet printhead that deforms a piezoelectric element and ejects ink using pressure applied to the ink by deformation of the piezoelectric element.
FIG. 1 illustrates a sectional view of a piezoelectric inkjet printhead. Referring to FIG. 1, a manifold 2, a plurality of restrictors 3, a plurality of pressure chambers 4, and a plurality of nozzles 5, which together constitute ink channels, may be formed inside a channel-forming plate 1. A plurality of piezoelectric actuators 6 may be mounted on the channel-forming plate 1. The manifold 2 is a passage for supplying ink flowing from an ink storage region (not shown) to each of the plurality of pressure chambers 4, and the restrictors 3 are passages through which ink flows from the manifold 2 to the pressure chambers 16. The pressure chambers 4 are filled with ink to be ejected. Each of the pressure chambers 16 changes its volume as a corresponding piezoelectric actuator 6 is driven, thereby creating the pressure change required for ejecting ink, or for drawing ink from the manifold 2.
The channel-forming plate 1 may be manufactured by processing a plurality of thin plates made of, e.g., a ceramic material, metal or a synthetic resin, to form the ink channels, and then stacking these plates. The piezoelectric actuators 6 are provided on each of the pressure chambers 4 and have a stacked structure that includes a piezoelectric layer and an electrode for applying a voltage to the piezoelectric layer. Portions of the channel-forming plate 1, i.e., the portions that constitute upper walls of each of the pressure chambers 4, serve as vibration plates 1a that are deformed by driving the corresponding piezoelectric actuator 6.
When the piezoelectric inkjet printhead is operated and the vibration plate 1a is deformed by the piezoelectric actuator 6, the volume of the pressure chamber 4 reduces, which generates a pressure change in the pressure chamber 4, so that ink contained in the pressure chamber 4 is ejected to the outside through the nozzle 5. Subsequently, when the vibration plate 1a is restored to its original shape by the piezoelectric actuator 6, the volume of the pressure chamber 4 increases, which generates a pressure change in the pressure chamber 4, i.e., a pressure drop, so that ink flows from the manifold 2 into the pressure chamber 4 through the corresponding restrictor 3.
FIG. 2 illustrates an exploded perspective view of another piezoelectric inkjet printhead. Referring to FIG. 2, the piezoelectric inkjet printhead may be formed by stacking and bonding a plurality of thin plates 11 through 16. As illustrated, a first plate 11 having a plurality of nozzles 11a for ejecting ink is disposed at the lowermost side of the printhead, a second plate 12 having a manifold 12a and ink ejection parts 12b is stacked on the first plate 11, and a third plate 13 having ink inflow parts 13a and ink ejection parts 13b is stacked on the second plate 12. In addition, the third plate 13 may have an ink inlet 17 for the flow of ink to the manifold 12a from an ink storage region (not shown).
A fourth plate 14 having ink inflow parts 14a and ink ejection parts 14b is stacked on the third plate 13, and a fifth plate 15, having a plurality of pressure chambers 15a whose ends respectively communicate with the ink inflow parts 14a and the ink ejection parts 14b, is stacked on the fourth plate 14. The ink inflow parts 13a and 14a serve as passages through which the ink flows from the manifold 12a to the pressure chambers 15a, and the ink ejection parts 12b, 13b, and 14b serve as passages through which the ink is ejected from the pressure chambers 15a to the nozzles 11a. A sixth plate 16 closing the upper portion of the pressure chambers 15a is stacked on the fifth plate 15, and drive electrodes 20 and piezoelectric layers 21 that constitute piezoelectric actuators are formed on the sixth plate 16. Therefore, the sixth plate 16 serves as a vibration plate that vibrates when the piezoelectric actuators are driven to change the volume of each of the pressure chambers 15a disposed beneath them by elastically deforming the sixth plate 16.
The first through third plates 11, 12 and 13 may be formed by, e.g., etching or press-processing a thin metal plate, and the fourth through sixth plates 14, 15 and 16 may be formed by, e.g., cutting and processing a thin plate of ceramic material. The second plate 12 where the manifold 12a is formed may be formed by, e.g., injection molding, by press-processing a thin plastic material or a film-type adhesive, or by screen-printing a paste-type adhesive. The piezoelectric layer 21 formed on the sixth plate 16 may be formed by, e.g., coating a ceramic material, in paste form, and sintering it.
To manufacture the piezoelectric inkjet printhead illustrated in FIG. 2, multiple processes are required to separately process each of a plurality of metal plates and ceramic plates. Further, these plates must be stacked and then bonded using an adhesive. Moreover, the number of plates constituting the printhead of FIG. 2 is relatively large, so the number of processes required for aligning the plates increases, which increases the likelihood of generating an alignment error. When an alignment error is generated, ink does not flow quickly through the ink channels, which reduces the ink ejecting performance of the printhead. In particular, when high density printheads are manufactured in an effort to improve printing resolution, the alignment process requires significant accuracy, which leads to high manufacturing costs.
Since the plurality of plates constituting the printhead are manufactured by different methods using different materials, the manufacturing processes are complicated and bonding between materials of different kinds may be difficult, which reduces product yield. Also, even when the plurality of plates are accurately aligned and bonded during the manufacturing process, an alignment error or deformation may be generated due to a difference in thermal expansion coefficients between materials of different kinds when the temperature the materials change.
FIG. 3 illustrates an exploded perspective view of still another piezoelectric inkjet printhead. Referring to FIG. 3, the inkjet printhead has a structure in which three silicon substrates 30, 40 and 50 are stacked and bonded together. Pressure chambers 32 of a predetermined depth are formed in the lower surface of the upper substrate 30. An ink inlet 31 connected with an ink storage region (not shown) is formed to pass through one side of the upper substrate 30. The pressure chambers 32 are arranged in two columns along both sides of a manifold 41, which is formed in the intermediate substrate 40. Piezoelectric actuators 60 each providing a driving force required for ejecting ink to each of the pressure chambers 32 are formed on the upper surface of the upper substrate 30.
The intermediate substrate 40 has the manifold 41 connected to the ink inlet 31, and a plurality of restrictors 42, each of which is connected with a corresponding pressure chamber 32, are formed along both sides of the manifold 41. Also, each of a plurality of dampers 43 is formed in a position of the intermediate substrate 40 that corresponds to each of the pressure chambers 32. Each of the plurality of dampers 43 is formed to vertically pass through the intermediate substrate 40. Also, nozzles 51, each of which is connected with each of the dampers 43, are formed in the lower substrate 50.
As described above, the inkjet printhead illustrated in FIG. 3 has a structure in which only three silicon substrates 30, 40 and 50 are stacked. Therefore, the inkjet printhead of FIG. 3 has a reduced number of substrates compared with the inkjet printhead of FIG. 2, and thus the manufacturing process thereof is relatively simple. Accordingly, alignment errors arising during the process of stacking the three substrates may be reduced. However, the manufacturing cost of the printhead of FIG. 3 is still high, and the performance thereof at high driving frequencies for rapid printing may not be satisfactory.